Time-Delay Resilient Cooperative Filters for Cyber-Physical Systems

Reliable real-time and uninterrupted data tele-communication between subsystems in a Cyber Physical System (CPS) is at the core of secure operation of the CPS. Time-delay and Denial-of-Service (DoS) cyberattacks are among CPS cyber threats that could impair normal functioning in the CPS, through intentional latency in the data tele-communication systems by infliction of data congestion, routing issues, parasitic electro-magnetic interference, etc. Load Frequency Control (LFC) in smart grids are among critical CPS controllers where certain time-delays in the transmission of remote system parameters could cause instability and pervasive havocs within seconds, if not detected and contained promptly. This paper considers a general interconnected CPS of heterogenous subsystems where information is randomly delayed from one subsystem to another. The paper circumvents time-delays caused at the tele-communication layer by augmenting a Multi-Agent System (MAS) of cooperative filters that restore random information delays with negligible and controllable time-delays. Consequently, real-time information would be accessible by the subsystem controllers at all times, regardless of the delays inflicted in the tele-communication layer. The LFC problem has been considered as an example of a challenging CPS that is highly vulnerable to time-delay cyberattacks, and the proposed cooperative filters were used to validate the theoretical results through numerical simulations.